U.S. patent application number 13/937897 was filed with the patent office on 2014-01-23 for electric leakage detecting apparatus.
The applicant listed for this patent is KEIHIN CORPORATION. Invention is credited to Hidefumi ABE, Takeshi YAMADA.
Application Number | 20140021961 13/937897 |
Document ID | / |
Family ID | 49946025 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140021961 |
Kind Code |
A1 |
YAMADA; Takeshi ; et
al. |
January 23, 2014 |
ELECTRIC LEAKAGE DETECTING APPARATUS
Abstract
An electric leakage detecting apparatus, in an electric leakage
detecting apparatus which is insulated from a chassis ground and
detects electric leakages of a battery, is provided with: a voltage
dividing circuit that divides an output voltage of the battery; an
electric leakage determining circuit provided at a rear stage of
the voltage dividing circuit, that determines the presence of an
electric leakage based on a voltage detected by a circuit that
respectively connects to a positive electrode side insulation
resistance or a negative electrode side insulation resistance of
the battery; and a dark current inhibit circuit in which a switch
and a resistance are connected in parallel, that is inserted
between at least either one of wiring that connects a positive
terminal of the battery and the voltage dividing circuit, and
wiring that connects a negative terminal of the battery and the
voltage dividing circuit.
Inventors: |
YAMADA; Takeshi; (Tokyo,
JP) ; ABE; Hidefumi; (Sendai-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KEIHIN CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
49946025 |
Appl. No.: |
13/937897 |
Filed: |
July 9, 2013 |
Current U.S.
Class: |
324/503 |
Current CPC
Class: |
G01R 31/52 20200101;
G01R 31/382 20190101; G01R 31/50 20200101 |
Class at
Publication: |
324/503 |
International
Class: |
G01R 31/02 20060101
G01R031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2012 |
JP |
2012-159699 |
Claims
1. An electric leakage detecting apparatus, in an electric leakage
detecting apparatus which is insulated from a chassis ground and
detects electric leakages of a battery, provided with: a voltage
dividing circuit that divides an output voltage of the battery; an
electric leakage determining circuit provided at a rear stage of
the voltage dividing circuit, that determines the presence of an
electric leakage based on a voltage detected by a circuit that
respectively connects to a positive electrode side insulation
resistance or a negative electrode side insulation resistance of
the battery; and a dark current inhibit circuit in which a switch
and a resistance are connected in parallel, that is inserted
between at least either one of a wiring that connects a positive
terminal of the battery and the voltage dividing circuit, and a
wiring that connects a negative terminal of the battery and the
voltage dividing circuit.
2. An electric leakage detecting apparatus according to claim 1,
wherein the electric leakage determining circuit selectively
switches a path of electric current that flows to a capacitor which
is insulated from the chassis ground, between: a first path that is
not connected to the positive electrode side insulation resistance
and the negative electrode side insulation resistance of the
battery, a second path that is connected to the positive electrode
side insulation resistance, and a third path that is connected to
the negative electrode side insulation resistance, and determines
the presence of an electric leakage based on a voltage charged to
the capacitor by the first path, the second path, and the third
path, respectively.
3. An electric leakage detecting apparatus according to claim 1,
wherein resistances that constitute the voltage dividing circuit
all have the same resistance value.
4. An electric leakage detecting apparatus according to claim 2,
wherein the electric leakage determining circuit, at the time a
voltage charged to the capacitor is detected, disconnects an
electrical connection between its circuit and the voltage dividing
circuit.
5. An electric leakage detecting apparatus according to claim 2,
wherein the switch of the dark current inhibit circuit becomes an
ON state during the time period wherein one among the first path,
the second path, and the third path is selected as the path in
which the electric current flows to the capacitor, and the
capacitor is being charged, and becomes an OFF state during other
time periods thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Priority is claimed on Japanese Patent Application No.
2012-159699, filed Jul. 18, 2012, the content of which is
incorporated herein by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to an electric leakage
detecting apparatus.
[0004] 2. Description of Related Art
[0005] As is well known, vehicles such as electric vehicles and
hybrid vehicles are equipped with a motor, which becomes the source
of power, and a high voltage and large capacity battery that
supplies electric power to the motor. The high voltage battery is
one configured by serially connecting a plurality of battery cells
comprising lithium ion batteries or hydrogen nickel batteries, or
the like.
[0006] Such high voltage batteries for driving a motor are
insulated from the chassis ground for safety. Therefore, it is very
important to monitor the insulated state (or in other words, to
detect electric leakages) between the high voltage battery and the
chassis ground. Japanese Unexamined Patent Application, First
Publication No. 2011-102788 discloses a technique for monitoring
the insulated state between a high voltage battery and a chassis
ground by using the flying capacitor method.
SUMMARY
[0007] In the technique described in Japanese Unexamined Patent
Application, First Publication No. 2011-102788, high voltage
resistance circuit components become necessary the more the output
voltage of the battery becomes a high voltage, and there is a
problem in that the apparatus costs increase. Furthermore, with the
battery becoming a high voltage, degradation of the battery may
proceed due to the flowing of a large dark current.
[0008] Aspects of the present invention take into consideration the
above circumstances, with an object of providing an electric
leakage detecting apparatus that is able to inhibit the degradation
of a battery due to the dark current, while keeping an increase in
apparatus costs to a minimum.
[0009] The aspects of the present invention employ the following
configuration in order to solve the above problems.
[0010] (1) An electric leakage detecting apparatus of one aspect of
the present invention, in an electric leakage detecting apparatus
which is insulated from a chassis ground and detects electric
leakages of a battery, is provided with: a voltage dividing circuit
that divides an output voltage of the battery; an electric leakage
determining circuit provided at a rear stage of the voltage
dividing circuit, that determines the presence of an electric
leakage based on a voltage detected by a circuit that respectively
connects to a positive electrode side insulation resistance or a
negative electrode side insulation resistance of the battery; and a
dark current inhibit circuit in which a switch and a resistance are
connected in parallel, that is inserted between at least either one
of a wiring that connects a positive terminal of the battery and
the voltage dividing circuit, and a wiring that connects a negative
terminal of the battery and the voltage dividing circuit.
[0011] (2) In the aspect of (1) above, the electric leakage
determining circuit may selectively switch a path of electric
current that flows to a capacitor which is insulated from the
chassis ground, between: a first path that is not connected to the
positive electrode side insulation resistance and the negative
electrode side insulation resistance of the battery, a second path
that is connected to the positive electrode side insulation
resistance, and a third path that is connected to the negative
electrode side insulation resistance, and determine the presence of
an electric leakage based on a voltage charged to the capacitor by
the first path, the second path, and the third path,
respectively.
[0012] (3) In the aspect of (1) or (2) above, resistances that
constitute the voltage dividing circuit may all have the same
resistance value.
[0013] (4) In the aspect of (2) or (3) above, the electric leakage
determining circuit may, at the time a voltage charged to the
capacitor is detected, disconnect an electrical connection between
its circuit and the voltage dividing circuit.
[0014] (5) In the aspect of any one from (2) to (4) above, the
switch of the dark current inhibit circuit may become an ON state
during the time period wherein one among the first path, the second
path, and the third path is selected as the path in which the
electric current flows to the capacitor, and the capacitor is being
charged, and may become an OFF state during other time periods
thereof.
[0015] According to the above aspects of the present invention, the
voltage dividing circuit that divides the output voltage of the
battery is provided at a front stage of the electric leakage
determining circuit. Therefore, the withstanding voltage of the
circuit components that constitute the electric leakage determining
circuit can be lowered (or in other words, the electric leakage
determining circuit can be constituted by inexpensive circuit
components). In the present invention, component costs are required
to the extent that the voltage dividing circuit and the dark
current inhibit circuit are provided. However, as mentioned above,
since the electric leakage determining circuit can be constituted
by inexpensive circuit components, the increase in the apparatus
costs in total can be kept to a minimum.
[0016] Furthermore, according to the above aspects of the present
invention, the dark current inhibit circuit in which the switch and
the resistance are connected in parallel, is inserted between at
least either the wiring that connects the positive terminal of the
battery and the voltage dividing circuit, and the wiring that
connects the negative terminal of the battery and the voltage
dividing circuit. Therefore generation of the dark current can be
inhibited.
[0017] That is to say, according to the aspects of the present
invention, it becomes possible to inhibit the degradation of the
battery due to the dark current, while keeping the increase in
apparatus costs to a minimum.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic block diagram of an electric leakage
detecting apparatus 1 of an embodiment according to the present
invention.
[0019] FIG. 2 is a timing chart showing the temporal changes of the
ON/OFF state of switches SW1 to SW6 provided in the electric
leakage detecting apparatus 1.
[0020] FIG. 3 is a drawing showing the path (first path) of the
electric current flowing to a flying capacitor C at the time the
switches SW1, SW2, SW3, and SW4 are in an ON state.
[0021] FIG. 4A is a drawing showing the path (second path) of the
electric current flowing to the flying capacitor C at the time the
switches SW1, SW2, SW4, and SW5 are in an ON state, and the
switches SW3 and SW6 are in an OFF state.
[0022] FIG. 4B is a drawing showing the path (third path) of the
electric current flowing to the flying capacitor C at the time the
switches SW1, SW2, SW3, and SW6 are in an ON state, and the
switches SW4 and SW5 are in an OFF state.
DESCRIPTION OF THE EMBODIMENT
[0023] Herein, an embodiment of the present invention is described
with reference to the drawings.
[0024] FIG. 1 is a schematic block diagram of an electric leakage
detecting apparatus 1 according to the present embodiment. The
electric leakage detecting apparatus 1 is one that detects electric
leakages of a high voltage battery BT (a battery with a rated
voltage of 900 V for example) for driving a motor that is insulated
from a chassis ground BG, and is provided with a first dark current
inhibit circuit 2, a second dark current inhibit circuit 3, a
voltage dividing circuit 4, and an electric leakage determining
circuit 5.
[0025] The first dark current inhibit circuit 2 is constituted by a
switch SW1 with one end connected to the positive terminal of the
high voltage battery BT and the other end connected to the voltage
dividing circuit 4 (specifically a resistance R3 mentioned below),
and a resistance R1 connected in parallel to the switch SW1. The
second dark current inhibit circuit 3 is constituted by a switch
SW2 with one end connected to the negative terminal of the high
voltage battery BT and the other end connected to the voltage
dividing circuit 4 (specifically a resistance R5 mentioned below),
and a resistance R2 connected in parallel to the switch SW2.
[0026] In this manner, in the electric leakage detecting apparatus
1 of the present embodiment, dark current inhibit circuits
comprising a switch and a resistance connected in parallel are
inserted between both the wiring that connects the positive
terminal of the high voltage battery BT and the voltage dividing
circuit 4 (resistance R3), and the wiring that connects the
negative terminal of the high voltage battery BT and the voltage
dividing circuit 4 (resistance R5). The ON/OFF state of the switch
SW1 and the switch SW2 is controlled by a voltage detection circuit
6 provided in the electric leakage determining circuit 5 mentioned
below.
[0027] The voltage dividing circuit 4 is connected to the high
voltage battery BT via the first dark current inhibit circuit 2 and
the second dark current inhibit circuit 3, and is one that divides
the output voltage of the high voltage battery BT of for example
900 V, to approximately 600 V, for example, and is constituted by
the three resistances R3, R4, and R5.
[0028] One end of the resistance R3 is connected to the first dark
current inhibit circuit 2, and the other end is connected to one
end of the resistance R4 and the electric leakage determining
circuit 5 (specifically a switch SW3 mentioned below). One end of
the resistance R5 is connected to the second dark current inhibit
circuit 3, and the other end is connected to the other end of the
resistance R4 and the electric leakage determining circuit 5
(specifically a switch SW4 mentioned below). One end of the
resistance R4 is connected to the other end of the resistance R3,
and the other end is connected to the other end of the resistance
R5. The resistances R3, R4, and R5 that constitute the voltage
dividing circuit 4 all have the same resistance value.
[0029] The electric leakage determining circuit 5 is provided at a
rear stage of the voltage dividing circuit 4, and selectively
switches the path of the electric current that flows to a capacitor
insulated from the chassis ground BG, between: a first path that is
not connected to the positive electrode side insulation resistance
Rp and the negative electrode side insulation resistance Rn of the
high voltage battery BT, a second path that is connected to the
positive electrode side insulation resistance Rp, and a third path
that is connected to the negative electrode side insulation
resistance Rn. Then it determines the presence of an electric
leakage based on the voltage charged to the capacitor by the first
path, the second path, and the third path, respectively.
[0030] Such an electric leakage determining circuit 5 is
constituted by a flying capacitor C that corresponds to the
capacitor mentioned above, four switches SW3, SW4, SW5, and SW6,
four resistances R6, R7, R8, and R9, two diodes D1 and D2, and a
voltage detection circuit 6.
[0031] One end of the switch SW3 is connected to the voltage
dividing circuit 4 (the other end of the resistance R3), and the
other end is connected to one end of the switch SW5, the anode
terminal of the diode D1, and the cathode terminal of the diode D2.
One end of the switch SW4 is connected to the voltage dividing
circuit 4 (the other end of the resistance R5), and the other end
is connected to one end of the switch SW6, and one end of the
flying capacitor C.
[0032] One end of the flying capacitor C is connected to the other
end of the switch SW4 and one end of the switch SW6, and the other
end is connected to one end of the resistance R6 and one end of the
resistance R7. One end of the resistance R6 is connected to the
other end of the flying capacitor C, and the other end is connected
to the cathode terminal of the diode D1. One end of the resistance
R7 is connected to the other end of the flying capacitor C, and the
other end is connected to the anode terminal of the diode D2.
[0033] The anode terminal of the diode D1 is connected to the other
end of the switch SW3, one end of the switch SW5, and the cathode
terminal of the diode D2, and the cathode terminal is connected to
the other end of the resistance R6. The anode terminal of the diode
D2 is connected to the other end of the resistance R7, and the
cathode terminal is connected to the other end of the switch SW3,
one end of the switch SW5, and the anode terminal of the diode
D1.
[0034] One end of the switch SW5 is connected to the other end of
the switch SW3, the anode terminal of the diode D1, and the cathode
terminal of the diode D2, and the other end is connected to one end
of the resistance R8 and the voltage detection circuit 6. One end
of the switch SW6 is connected to the other end of the switch SW4
and one end of the flying capacitor C, and the other end is
connected to one end of the resistance R9.
[0035] One end of the resistance R8 is connected to the other end
of the switch SW5 and the voltage detection circuit 6, and the
other end is connected to the other end of the resistance R9, the
voltage detection circuit 6, and the chassis ground BG. One end of
the resistance R9 is connected to the other end of the switch SW6,
and the other end is connected to the other end of the resistance
R8, the voltage detection circuit 6, and the chassis ground BG.
[0036] The voltage detection circuit 6 is for example a digital
processor that executes various processes according to a program of
a microcomputer, and it controls the ON/OFF state of the switches
SW1 to SW6, to thereby have: a function of selectively switching
the path of the electric current that flows to the flying capacitor
C between the first path mentioned above that is not connected to
the positive electrode side insulation resistance Rp and the
negative electrode side insulation resistance Rn, the second path
that is connected to the positive electrode side insulation
resistance Rp, and the third path that is connected to the negative
electrode side insulation resistance Rn; and a function of
detecting the voltage charged to the flying capacitor C by the
first path, the second path, and the third path, respectively, and
determining the presence of an electrical leakage based on the
detection result thereof.
[0037] Hereunder is a description of the operation of the electric
leakage detecting apparatus 1 constituted as described above.
[0038] FIG. 2 is a timing chart showing the temporal changes of the
ON/OFF state of the switches SW1 to SW6 provided in the electric
leakage detecting apparatus 1. As shown in FIG. 2, at the time of
non-operation, that is to say, during the period when the electric
leakage detection operation is not executed (the period of time t1
to t2 in the figure), the voltage detection circuit 6 controls all
of the switches SW1 to SW6 to the OFF state.
[0039] When all of the switches SW1 to SW6 become the OFF state, an
electric current (dark current) flows along the path of the
positive terminal of the high voltage battery BT.fwdarw.the
resistance R1.fwdarw.the resistance R3.fwdarw.the resistance
R4.fwdarw.the resistance R5.fwdarw.the resistance R2.fwdarw.the
negative terminal of the high voltage battery BT. However the dark
current can be inhibited by setting the resistance values of the
resistance R1 of the first dark current inhibit circuit 2 and the
resistance R2 of the second dark current inhibit circuit 3 to a
large value.
[0040] Assuming that the electric leakage detection operation is
started from the time t2 in the figure, the voltage detection
circuit 6 firstly executes a total voltage charging process in the
period from time t2 to t3. Specifically, the voltage detection
circuit 6 controls the switches SW1, SW2, SW3, and SW4 to the ON
state within the period from time t2 to t3, to thereby switch the
path of the electric current that flows to the flying capacitor C
to the first path that is not connected to the positive electrode
side insulation resistance Rp and the negative electrode side
insulation resistance Rn.
[0041] When the switches SW1, SW2, SW3, and SW4 become the ON
state, then as shown in FIG. 3, an electric current flows along the
path (that is to say, the first path) of the positive terminal of
the high voltage battery BT--the switch SW1.fwdarw.the resistance
R3.fwdarw.the switch SW3.fwdarw.the diode D1.fwdarw.the resistance
R6.fwdarw.the flying capacitor C.fwdarw.the switch SW4.fwdarw.the
resistance R5.fwdarw.the switch SW2.fwdarw.the negative terminal of
the high voltage battery BT.
[0042] In such a manner, in a case where the switches SW1, SW2,
SW3, and SW4 are made the ON state, the combined resistance R of
the first path in which the electric current flows is represented
by formula (1) below. Furthermore, the voltage Vc (that is to say,
the inter-terminal voltage of the flying capacitor C) charged to
the flying capacitor C is represented by formula (2) below. In
formula (2) below, Vb is the output voltage of the high voltage
battery BT, and Ton1 is the charging time (Ton1=t3-t2) of the
flying capacitor C. Hereunder, the voltage Vc charged to the flying
capacitor C at the time of execution of the total voltage charging
process in the manner mentioned above is referred to as the total
voltage.
R = R 3 ( R 4 + R 5 ) + R 6 ( 1 ) Vc = Vb .times. R 4 ( R 3 + R 4 +
R 5 ) .times. { 1 - EXP ( - Ton 1 R .times. C ) } ( 2 )
##EQU00001##
[0043] Next, the voltage detection circuit 6 executes a total
voltage reading process in the period from time t3 to t4 in FIG. 2.
Specifically, the voltage detection circuit 6, within the period
from time t3 to t4, controls the switches SW1, SW2, SW3, and SW4 to
the OFF state, and controls the switches SW5 and SW6 to the ON
state, to thereby detect the inter-terminal voltage of the flying
capacitor C, that is to say, the total voltage Vc (converted to a
digital value and read in), and stores the detection result
(digital value of the total voltage Vc) thereof in an internal
memory.
[0044] In practice, the total voltage Vc is divided by the
resistances R7, R8, and R9, and read into the voltage detection
circuit 6 as the inter-terminal voltage of the resistance R8.
Consequently, the voltage detection circuit 6 converts the read in
inter-terminal voltage of the resistance R8, into the
inter-terminal voltage of the flying capacitor C, that is to say,
the total voltage Vc, based on the resistance values of the
resistances R7, R8, and R9.
[0045] Next, the voltage detection circuit 6 executes a positive
electrode side insulation resistance voltage charging process in
the period from time t4 to t5 in FIG. 2. Specifically, the voltage
detection circuit 6, within the period from time t4 to t5, controls
the switches SW1, SW2, SW4, and SW5 to the ON state, and controls
the switches SW3 and SW6 to the OFF state, to thereby switch the
path of the electric current that flows to the flying capacitor C
to the second path that is connected to the positive electrode side
insulation resistance Rp.
[0046] When the switches SW1, SW2, SW4, and SW5 become the ON
state, and the switches SW3 and SW6 become the OFF state, then as
shown in FIG. 4A, an electric current flows along the path (that is
to say, the second path) of the positive terminal of the high
voltage battery BT.fwdarw.the positive electrode side insulation
resistance Rp.fwdarw.the chassis ground BG.fwdarw.the resistance
R8.fwdarw.the switch SW5.fwdarw.the diode D1.fwdarw.the resistance
R6.fwdarw.the flying capacitor C.fwdarw.the switch SW4.fwdarw.the
resistance R5.fwdarw.the switch SW2.fwdarw.the negative terminal of
the high voltage battery BT.
[0047] In such a manner, in a case where the switches SW1, SW2,
SW4, and SW5 are made the ON state, and the switches SW3 and SW6
are made the OFF state, the combined resistance R(+) of the second
path in which the electric current flows is represented by formula
(3) below. Furthermore, the voltage Vcp charged to the flying
capacitor C is represented by formula (4) below. In formula (4)
below, Ton2 is the charging time (Ton2 =t5-t4) of the flying
capacitor C. Hereunder, the voltage Vcp charged to the flying
capacitor C at the time of execution of the positive electrode side
insulation resistance voltage charging process in the manner
mentioned above is referred to as the positive electrode side
insulation resistance voltage.
R ( + ) = ( R 3 + R 4 ) R 5 + R 6 + Rp Rn ( 3 ) Vcp = Vb .times. (
Rn Rp + Rn - R 5 R 3 + R 4 + R 5 ) .times. { 1 - EXP ( - Ton 2 R (
+ ) .times. C ) } ( 4 ) ##EQU00002##
[0048] Next, the voltage detection circuit 6 executes a positive
electrode side insulation resistance voltage reading process in the
period from time t5 to t6 in FIG. 2. Specifically, the voltage
detection circuit 6, within the period from time t5 to t6, controls
the switches SW1, SW2, SW3, and SW4 to the OFF state, and controls
the switches SW5 and SW6 to the ON state, to thereby detect the
inter-terminal voltage of the flying capacitor C, that is to say,
the positive electrode side insulation resistance voltage Vcp
(converted to a digital value and read in), and stores the
detection result (digital value of the positive electrode side
insulation resistance voltage Vcp) thereof in an internal
memory.
[0049] In the same manner as mentioned above, in practice, the
positive electrode side insulation resistance voltage Vcp is
divided by the resistances R7, R8, and R9, and read into the
voltage detection circuit 6 as the inter-terminal voltage of the
resistance R8. Consequently, the voltage detection circuit 6
converts the read in inter-terminal voltage of the resistance R8,
into the positive electrode side insulation resistance voltage Vcp,
based on the resistance values of the resistances R7, R8, and
R9.
[0050] Next, the voltage detection circuit 6 executes a total
voltage charging process again in the period from time t6 to t7 in
the figure. That is to say, the voltage detection circuit 6, within
the period from time t6 to t7, controls the switches SW1, SW2, SW3,
and SW4 to the ON state, to thereby switch the path of the electric
current that flows to the flying capacitor C to the first path.
Consequently, the total voltage Vc represented by formula (2)
mentioned above is charged to the flying capacitor C.
[0051] Next, the voltage detection circuit 6 executes a total
voltage reading process in the period from time t7 to t8 in FIG. 2.
That is to say, the voltage detection circuit 6, within the period
from time t7 to t8, controls the switches SW1, SW2, SW3, and SW4 to
the OFF state, and controls the switches SW5 and SW6 to the ON
state, to thereby detect the inter-terminal voltage of the flying
capacitor C, that is to say, the total voltage Vc (converted to a
digital value and read in), and stores the detection result
(digital value of the total voltage Vc) thereof in an internal
memory.
[0052] Next, the voltage detection circuit 6 executes a negative
electrode side insulation resistance voltage charging process in
the period from time t8 to t9 in FIG. 2. Specifically, the voltage
detection circuit 6, within the period from time t8 to t9, controls
the switches SW1, SW2, SW3, and SW6 to the ON state, and controls
the switches SW4 and SW5 to the OFF state, to thereby switch the
path of the electric current that flows to the flying capacitor C
to the third path that is connected to the negative electrode side
insulation resistance Rn.
[0053] When the switches SW1, SW2, SW3, and SW6 become the ON
state, and the switches SW4 and SW5 become the OFF state, then as
shown in FIG. 4B, an electric current flows along the path (that is
to say, the third path) of; the positive terminal of the high
voltage battery BT.fwdarw.the switch SW1.fwdarw.the resistance
R3.fwdarw.the switch SW3.fwdarw.the diode D1.fwdarw.the resistance
R6.fwdarw.the flying capacitor C.fwdarw.the switch SW6.fwdarw.the
resistance R9.fwdarw.the chassis ground BG.fwdarw.the negative
electrode side insulation resistance Rn.fwdarw.the negative
terminal of the high voltage battery BT.
[0054] In such a manner, in a case where the switches SW1, SW2,
SW3, and SW6 are made the ON state, and the switches SW4 and SW5
are made the OFF state, the combined resistance R(-) of the third
path in which the electric current flows is represented by formula
(5) below. Furthermore, the voltage Vcn charged to the flying
capacitor C is represented by formula (6) below. In formula (6)
below, Ton2 is the charging time (Ton2 =t9-t8) of the flying
capacitor C. Hereunder, the voltage Vcn charged to the flying
capacitor C at the time of execution of the negative electrode side
insulation resistance voltage charging process in the manner
mentioned above is referred to as the negative electrode side
insulation resistance voltage.
R ( - ) = ( R 4 + R 5 ) R 3 + R 6 + Rp Rn ( 5 ) Vcn = Vb .times. (
R 4 + R 5 R 3 + R 4 + R 5 - Rn Rp + Rn ) .times. { 1 - EXP ( - Ton
2 R ( - ) .times. C ) } ( 6 ) ##EQU00003##
[0055] Next, the voltage detection circuit 6 executes a negative
electrode side insulation resistance voltage reading process in the
period from time t9 to t10 in FIG. 2. Specifically, the voltage
detection circuit 6, within the period from time t9 to t10,
controls the switches SW1, SW2, SW3, and SW4 to the OFF state, and
controls the switches SW5 and SW6 to the ON state, to thereby
detect the inter-terminal voltage of the flying capacitor C, that
is to say, the negative electrode side insulation resistance
voltage Vcn (converted to a digital value and read in), and stores
the detection result (digital value of the negative electrode side
insulation resistance voltage Vcn) thereof in an internal
memory.
[0056] In the same manner as mentioned above, in practice, the
negative electrode side insulation resistance voltage Vcn is
divided by the resistances R7, R8, and R9, and read into the
voltage detection circuit 6 as the inter-terminal voltage of the
resistance R8. Therefore, the voltage detection circuit 6 converts
the read in inter-terminal voltage of the resistance R8, into the
negative electrode side insulation resistance voltage Vcn, based on
the resistance values of the resistances R7, R8, and R9.
[0057] The voltage detection circuit 6 calculates the insulation
resistance value based on the total voltage Vc, the positive
electrode side insulation resistance voltage Vcp, and the negative
electrode side insulation resistance voltage Vcn, obtained by the
processes executed in the periods from time t2 to t10 as mentioned
above, and determines that an electrical leakage has occurred in a
case where the calculated insulation resistance value thereof is
less than a threshold value. When R2=R4, R(+)=R(-)=R. Therefore
Vcn+Vcp is represented by formula (7) below, and the insulation
resistance value is represented by formula (8) below.
Vcn + Vcp = Vb .times. R 4 R 3 + R 4 + R 5 .times. { 1 - EXP ( -
Ton 2 R .times. C ) } ( 7 ) Ratio of insulation resistance values =
Rp Rn = - Ton 2 C .times. 1 LN { 1 - R 3 + R 4 + R 5 R 3 .times. Vb
.times. ( Vcn + Vcp ) } - R 3 + R 4 R 2 - R 6 ( 8 )
##EQU00004##
[0058] In the above manner, according to the present embodiment,
the voltage dividing circuit 4 that divides the output voltage of
the high voltage battery BT, is provided at a front stage of the
electric leakage determining circuit 5. Therefore, the withstanding
voltage of the circuit components that constitute the electric
leakage determining circuit 5 can be lowered (or in other words,
the electric leakage determining circuit 5 can be constituted by
inexpensive circuit components). In the present embodiment,
component costs are required to the extent that the voltage
dividing circuit 4 and the dark current inhibit circuits 2 and 3
are provided. However, as mentioned above, since the electric
leakage determining circuit 5 can be constituted by inexpensive
circuit components, the increase in the apparatus costs in total
can be kept to a minimum.
[0059] Furthermore, according to the present embodiment, the dark
current inhibit circuits 2 and 3 in which the switches and the
resistances are connected in parallel, are inserted between, at
least, both the wiring that connects the positive terminal of the
high voltage battery BT and the voltage dividing circuit 4, and the
wiring that connects the negative terminal of the high voltage
battery BT and the voltage dividing circuit 4. Therefore generation
of the dark current can be inhibited. That is to say, according to
the electric leakage detecting apparatus 1 of the present
embodiment, it becomes possible to inhibit the degradation of the
battery due to the dark current, while keeping the increase in
apparatus costs to a minimum.
[0060] Further, the electric leakage detection accuracy decreases
if the resistance values of the resistances R3, R4, and R5 that
constitute the voltage dividing circuit 4 become too small.
However, by making the resistance values of the resistances R3, R4,
and R5 that constitute the voltage dividing circuit 4 all the same
in the manner of the present embodiment, the electric leakage
detection accuracy can be maintained.
[0061] Moreover, at the time the voltage charged to the flying
capacitor C is detected, the switches SW1, SW2, SW3, and SW4 are
made the OFF state, the switches SW5 and SW6 are made the ON state,
and the electrical connection between the electric leakage
determining circuit 5 and the voltage dividing circuit 4 is
disconnected. As a result, the application of a voltage to the
switches SW5 and SW6 that exceeds the withstanding voltage can be
avoided.
[0062] The present invention is in no way limited by the embodiment
mentioned above. For example, in the embodiment mentioned above, a
case in which the dark current inhibit circuits 2 and 3 are
inserted between both the wiring that connects the positive
terminal of the high voltage battery BT and the voltage dividing
circuit 4, and the wiring that connects the negative terminal of
the high voltage battery BT and the voltage dividing circuit 4 is
exemplified. However, even if either one of the dark current
inhibit circuits 2 and 3 is inserted between just one of the
wirings, their effect is exerted.
[0063] Furthermore, in the embodiment mentioned above, the electric
leakage determining circuit 5 of a so-called flying capacitor
method that selectively switches the path of the electric current
that flows to the flying capacitor C between; the first path that
is not connected to the positive electrode side insulation
resistance Rp and the negative electrode side insulation resistance
Rn, the second path that is connected to the positive electrode
side insulation resistance Rp, and the third path that is connected
to the negative electrode side insulation resistance Rn, and
determines the presence of an electric leakage based on the voltage
charged to the flying capacitor C at the first path, the second
path, and the third path, respectively, is exemplified. The present
invention is in no way limited to this, and an electric leakage
determining circuit (for example an electric leakage determining
circuit of a resistance dividing method) that determines the
presence of an electric leakage based on the voltage detected in a
path that is respectively connected to the positive electrode side
insulation resistance Rp or the negative electrode side insulation
resistance Rn of the high voltage battery BT may be employed.
* * * * *